The invention relates generally to catheters, and more particularly to a catheter having a steerable distal-end region with enhanced distal torque transfer.
The heart beat in a healthy human is controlled by the sinoatrial node (xe2x80x9cS-A nodexe2x80x9d) located in the wall of the right atrium. The S-A node generates electrical signal potentials that are transmitted through pathways of conductive heart tissue in the atrium to the atrioventricular node (xe2x80x9cA-V nodexe2x80x9d) which in turn transmits the electrical signals throughout the ventricle by means of the His and Purkinje conductive tissues. Improper growth of, or damage to, the conductive tissue in the heart can interfere with the passage of regular electrical signals from the S-A and A-V nodes. Electrical signal irregularities resulting from such interference can disturb the normal rhythm of the heart and cause an abnormal rhythmic condition referred to as xe2x80x9ccardiac arrhythmia.xe2x80x9d
While there are different treatments for cardiac arrhythmia, including the application of anti-arrhythmia drugs, in many cases ablation of the damaged tissue can restore the correct operation of the heart. Such ablation can be performed by percutaneous ablation, a procedure in which a catheter is percutaneously introduced into the patient and directed through an artery or vein to the atrium or ventricle of the heart to perform single or multiple diagnostic, therapeutic, and/or surgical procedures. In such case, an ablation procedure is used to destroy the tissue causing the arrhythmia in an attempt to remove the electrical signal irregularities or create a conductive tissue block to restore normal heart beat or at least an improved heart beat. Successful ablation of the conductive tissue at the arrhythmia initiation site usually terminates the arrhythmia or at least moderates the heart rhythm to acceptable levels. A widely accepted treatment for arrhythmia involves the application of RF energy to the conductive tissue.
In the case of atrial fibrillation (xe2x80x9cAFxe2x80x9d), a procedure published by Cox et al. and known as the xe2x80x9cMaze procedurexe2x80x9d involves continuous atrial incisions to prevent atrial reentry and to allow sinus impulses to activate the entire myocardium. While this procedure has been found to be successful, it involves an intensely invasive approach. It is more desirable to accomplish the same result as the Maze procedure by use of a less invasive approach, such as through the use of an appropriate electrophysiological (xe2x80x9cEPxe2x80x9d) catheter system.
One such EP catheter system, as disclosed in U.S. Pat. Nos. 6,059,778 and 6,096,036, includes a plurality of spaced apart band electrodes located at the distal end of the catheter and arranged in a linear array. The band electrodes are positioned proximal heart tissue. RF energy is applied through the electrodes to the heart tissue to produce a series of long linear lesions similar to those produced by the Maze procedure. The catheters currently used for this procedure are typically flexible at the distal end, and the profile at the distal end is adjustable. However, when using such catheters, it is often difficult to conform the distal-end profile to some of the irregular topographies of the interior cavities of the heart. In other instances, it is difficult for a multi-electrode catheter that is designed to produce long linear lesions to access and ablate tissue in regions that require short linear lesions, such as the so-called isthmus region that runs from the tricuspid annulus to the eustachian ridge. Ablation of tissue in this region, and other regions non-conducive to the placement of multi-electrode, long, linear-lesion ablation catheters within them, is best accomplished by delivering RF energy to a tip electrode to produce localized spot lesions or if longer lesions are required, by energizing the tip while it is moved across the tissue.
Other catheters for producing spot lesions or tip-drag lesions typically include a tip ablation electrode and a plurality of mapping band electrodes positioned at the distal end of the catheter. The catheters are steerable in that they are configured to allow the profile of the distal end of the catheter to be manipulated from a location outside the patient""s body. Steerable catheters that produce multiple deflection profiles of their distal ends provide a broader range of steerability. However, known steerable catheters, such as that disclosed in U.S. Pat. No. 5,195,968, have steering tendons attached to a ribbon at or near the longitudinal centerline of the catheter. Because of the relatively short distance between the tendon attachment point and the ribbon that resides along the centerline of the catheter sheath, a force applied to the tendon results in a relatively small bending moment for deflecting the distal tip. The ribbon/tendon assembly is typically provided clearance to allow the tendon to become substantially displaced from the centerline as deflection progresses, thereby enlarging the moment arm and consequently increasing the applied bending moment. Unfortunately, this requires such designs to include additional lumen space, translating into larger catheter diameters. Larger diameter catheters are undesirable due to the increased trauma they inflict on a patient. Further, as the tendon displaces to the extent that it contacts the catheter wall, the associated friction may necessitate greater exertion to further deflect the distal tip. Lessening the amount of force required to deflect the distal tip of a catheter by actions outside the catheter is desired in that the catheter tip can more easily be placed in the correct location within a patient.
In addition to deflecting the distal tip, placing the distal portion of a catheter in the correct location within a patient often requires rotation of the catheter from a location outside the body, typically by rotating the handle. However, the sheaths in known steerable catheters have proximal regions with higher torsional strength than their distal-end regions. The reduction in torsional strength from the proximal region to the distal-end region makes accurate rotation of the distal portion difficult and if not carefully controlled, can result in a whip effect of the distal tip. Uncontrolled movement of the distal tip can cause trauma to the patient.
Hence, those skilled in the art have identified a need for a tip-electrode, ablation catheter with a steerable distal-end region that is capable of accessing those areas of the heart which are typically inaccessible by multi-electrode ablation catheters. Needs have also been identified for smaller diameter catheters to improve patient comfort, and for more easily deflected catheters so that they may be more easily used. Additionally, the need for a catheter having sufficient torsional stiffness at its distal end to permit more accurate transfer of rotational movement from the handle to the distal tip has also been identified. The present invention fulfills these needs and others.
Briefly, and in general terms, the present invention is directed to a catheter with a steerable distal-end region and enhanced distal torque transfer.
In a first aspect, the invention relates to a catheter that includes a sheath having a proximal region, a distal-end region, and a longitudinal centerline. The catheter also includes a first steering tendon housed within the sheath. The first steering tendon has a first end that is attached to the distal-end region at a location offset from the centerline of the sheath, and a second end that is located at the proximal region of the sheath. Movement of the first steering tendon in the proximal direction causes the sheath distal-end region to deflect. The catheter further includes a second steering tendon housed within the sheath. The second steering tendon has a first end that is attached to the distal-end region at a location offset from the centerline of the sheath, and a second end that is located at the proximal region of the sheath. Movement of the second steering tendon in the proximal direction causes the sheath distal-end region to deflect. Additionally, the catheter also includes a torque transfer system that is adapted to transfer torsional forces from the proximal region of the sheath to the distal-end region of the sheath.
In a detailed aspect of the invention, the torque transfer system includes a ribbon that is housed within the distal-end region of the sheath. The ribbon is configured to deflect with the distal-end region of the sheath and has a first end attached to the distal-end region of the sheath and a second end attached to the proximal region of the sheath. In a more detailed aspect, the ribbon is positioned along the centerline of the distal-end region of the sheath. In a further detailed aspect, the ribbon is formed of a resiliently deformable, shape-memory material. In another detailed aspect, the ribbon has a substantially rectangular cross-section and the first steering tendon and the second steering tendon are attached proximate the inner surface of the sheath on opposite sides of the ribbon. In another facet of the invention, the attachment point of the first steering tendon is distal the attachment point of the second steering tendon. In an additional detailed facet, the attachment point of the first steering tendon and the attachment point of the second steering tendon are axially aligned. In a further facet of the invention, the ribbon has a substantially rectangular cross-section and the first steering tendon and the second steering tendon are attached proximate the inner surface of the sheath on the same side of the ribbon. In another aspect of the invention, the torque transfer system further includes an eyelet secured within the proximal region of the sheath and the second end of the ribbon is secured within the eyelet. In a more detailed aspect, the eyelet includes a non-circular shape proximal end having a maximum cross-sectional diameter greater than the inner diameter of the sheath. In a further aspect, the non-circular shape includes a substantially angular shape. In a more detailed aspect, the angular shape includes a substantially hexagonal shape.
In a second aspect, the invention relates to a catheter that includes a sheath having a proximal region and a distal-end region. The catheter also includes a first steering tendon that is housed within the sheath. The first steering tendon has a first end that is attached to the distal-end region at a point proximate the inner surface of the sheath, and a second end that exits the proximal end of the sheath. Movement of the first steering tendon in a proximal direction causes the sheath distal-end region to deflect. The catheter further includes a second steering tendon that is housed within the sheath. The second steering tendon has a first end that is attached to the distal-end region at a point proximate the inner surface of the sheath and proximal the attachment point of the first steering tendon, and a second end that exits the proximal end of the sheath. Movement of the second steering tendon in the proximal direction causes the sheath distal-end region to deflect. Additionally, the catheter also includes a ribbon that is housed within the distal-end region of the sheath and is configured to deflect therewith. The ribbon has a first end that is attached to the distal-end region of the sheath and a second end that is attached to the proximal region of the sheath.
In a detailed aspect of the invention, the ribbon has a substantially rectangular cross-section and the first and second steering tendons are attached on opposite sides of the ribbon. In another aspect, the ribbon has a substantially rectangular cross-section and the first steering tendon and the second steering tendon are attached on the same side of the ribbon. In a more detailed aspect, the first end of the ribbon is secured within the distal tip of the distal-end region. In another facet of the invention, the catheter further includes an eyelet that is housed within the proximal region of the sheath at the distal end of the proximal region wherein the second end of the ribbon is secured within the eyelet. In a further facet, the first steering tendon is secured within the distal tip of the distal-end region. In an additional facet, the catheter further includes an anchor band that is positioned within the distal-end region, proximal the distal tip, wherein the first end of the second steering tendon is attached to the anchor band.
In a third aspect, the invention relates to a catheter for use with biological tissue. The catheter includes a sheath having a proximal region with a first torque transfer strength and a distal-end region with a second torque transfer strength that is less than the first torque transfer strength. The catheter further includes at least one electrode that is located in the distal-end region for transferring energy to the biological tissue. The catheter additionally includes a first steering tendon that is housed within the sheath. The first steering tendon has a first end that is attached to the distal-end region at a point proximate the inner surface of the sheath and a second end that exits the proximal end of the sheath. Movement of the first steering tendon in a proximal direction causes the sheath distal-end region to deflect. The catheter also includes a second steering tendon that is housed within the sheath. The second steering tendon has a first end that is attached to the distal-end region at a point proximate the inner surface of the sheath and proximal to the attachment point of the first steering tendon and a second end that exits the proximal end of the sheath. Movement of the second steering tendon in the proximal direction causes the sheath distal-end region to deflect. The catheter further includes a torque transfer system that is adapted to increase the torque transfer strength of the distal-end region to facilitate the transfer of torsional forces from the proximal region to the distal-end region.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.